Method For Producing Nickel-Containing Films

ABSTRACT

Provided are precursors and methods of using same to deposit film consisting essentially of nickel. Certain methods comprise providing a substrate surface; exposing the substrate surface to a vapor comprising a precursor having a structure represented by formula (I): 
     
       
         
         
             
             
         
       
     
     wherein R 1  is t-butyl and each R 2  is each independently any C1-C3 alkyl group; and exposing the substrate to a reducing gas to provide a film consisting essentially of nickel on the substrate surface.

TECHNICAL FIELD

The present invention relates generally to methods of depositing thinfilms of metal. In particular, the invention relates to the use ofcoordination complexes containing nickel to deposit films consistingessentially of nickel.

BACKGROUND

Deposition of thin films on a substrate surface is an important processin a variety of industries including semiconductor processing, diffusionbarrier coatings and dielectrics for magnetic read/write heads. In thesemiconductor industry, in particular, miniaturization requires atomiclevel control of thin film deposition to produce conformal coatings onhigh aspect structures. One method for deposition of thin films chemicalvapor deposition (CVD). In this process, a wafer is typically exposed toone or more volatile precursors, which react to deposit a films. Arelated process is atomic layer deposition (ALD), which employssequential surface reactions to form layers of precise thicknesscontrolled at the Angstrom or monolayer level. Most ALD processes arebased on binary reaction sequences which deposit a binary compound film.Because the surface reactions are sequential, the two gas phasereactants are not in contact, and possible gas phase reactions that mayform and deposit particles are limited.

There is a need for new deposition chemistries that are commerciallyviable, particularly in the area of elemental metal films, includingnickel films for nickel silicide contacts. For example, nickel filmshave been deposited using Ni(PF₃)₄ and bis(cyclopentadienyl)Nicoordination complexes. However, each of these complexes has presentedproblems. Ni(PF₃)₄ is toxic and bis(cyclopentadienyl)Ni can lead tocarbon contamination in the film. The present invention addresses theseproblems by providing novel chemistries.

SUMMARY

One aspect of the invention relates to a method of depositing a filmconsisting essentially of nickel. The method comprises providing asubstrate surface; exposing the substrate surface to a vapor comprisinga precursor having a structure represented by:

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup; and exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface. Variousembodiments are listed below. It will be understood that the embodimentslisted below may be combined not only as listed below, but in othersuitable combinations in accordance with the scope of the invention.

In one or more embodiments, R² is methyl. In alternative embodiments, R²is C2 or C3 alkyl. In one or more embodiments, the precursor ishomoleptic. In some embodiments, the substrate comprises silicon. One ormore embodiments relates to where the substrate surface is exposed tothe precursor and reductant gas substantially simultaneously orsequentially. In some embodiments, the reducing gas comprises ammoniagas or hydrogen gas. In one or more embodiments, the film consistingessentially of nickel contains no oxygen.

A second aspect of the invention relates to a method of depositing afilm consisting essentially of nickel via atomic layer deposition, themethod comprising: providing a substrate surface comprising silicon,wherein the substrate surface has a temperature ranging from betweenabout 120 and about 250° C.; sequentially exposing the substrate surfaceto vapor comprising a precursor having a structure represented by:

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup; and exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface.

Many of the same variants as used in the previous aspect can also beapplied here. Thus, for example, in one or more embodiments, R² ismethyl. In some embodiments, the precursor is homoleptic. In one or moreembodiments, exposure of the substrate surface to the vapor comprisingthe precursor and the reducing gas occurs under an oxide-freeenvironment. In some embodiments, five, the reducing gas comprisesammonia gas or hydrogen gas. One or more embodiments relates to wherethe film consists essentially of nickel is oxide-free and contains lessthan about 5% carbon.

A third aspect of the invention relates to a method of depositing a filmconsisting essentially of nickel via chemical vapor deposition, themethod comprising providing a substrate surface comprising silicon;simultaneously exposing the substrate surface to a vapor comprising aprecursor having a structure represented by:

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup while exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface.

Again, many of the same variants as used in the previous aspects canalso be applied here. Thus, for example, in one or more embodiments, R²is methyl. In some embodiments, exposure of the substrate surface to thevapor comprising the precursor and the reducing gas occurs under anoxide-free environment. In one or more embodiments, the precursor ishomoleptic. Some embodiments relate to where the reducing gas comprisesammonia gas or hydrogen gas. One or more embodiments relate to where thefilm consists essentially of nickel is oxide free and contains less thanabout 5% carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a thermogravimetric analysis of two metal coordinationcomplexes.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways. It is also to be understood that thecomplexes and ligands of the present invention may be illustrated hereinusing structural formulas which have a particular stereochemistry. Theseillustrations are intended as examples only and are not to be construedas limiting the disclosed structure to any particular stereochemistry.Rather, the illustrated structures are intended to encompass all suchcomplexes and ligands having the indicated chemical formula.

As used herein, the term “consisting essentially of nickel” means thatdeposited layer contains mostly elemental nickel. In one or moreembodiments, small amounts of impurities are within the meaning of theterm. In one or more embodiments, the film contains no oxygen, and/orcontains less than 5% carbon.

The term “metal coordination complex” as used herein is usedinterchangeably with “metal complex” and “coordination complex,” andincludes structures that consist of a central metal atom bonded to oneor more ligands. As will be discussed in more detail below, the metalcomplexes of the invention comprise of pyrrolyl-based ligandscoordinated to nickel atoms.

One aspect of the invention relates to such a metal coordinationcomplex. The metal coordination complex has a structure represented byformula (I):

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup. In one embodiment, R² is methyl. In an alternative embodiment, R²is C2 or C3 alkyl. In one or more embodiments, the precursor ishomoleptic.

The precursors described herein are alternatives to previously usedprecursors like Ni(PF₃)₄ and bis(cyclopentadienyl)nickel. The precursorsaccording to formula (I) above are lower toxicity, but cost competitiveas compared to Ni(PF₃)₄. The precursors are also likely to results inless carbon contamination than previously usedbis(cyclopentadienyl)nickel complexes.

The synthesis of this metal coordination complex begins with theproduction of the pyrrole-based ligand according to known methods in theart. The pyrrole-based ligand is then treated with butyllithium to formthe pyrrolide, which is then reacted with a nickel halide to form thebis(pyrrolyl)nickel precursor. An exemplary synthesis scheme is shownbelow as Schematic 1:

The properties of a specific metal coordination complex for use in theALD deposition methods of the invention can be evaluated using methodsknown in the art, allowing selection of appropriate temperature andpressure for the reaction. In general, lower molecular weight and thepresence of functional groups result in a melting point that yieldsliquids at typical delivery temperatures and increased vapor pressure.

In one or more embodiments, these metal coordination complexes areuseful to deposit thin films consisting essentially of nickel. Thus,another aspect of the invention relates to a method of depositing a filmconsisting essentially of nickel. The method comprises providing asubstrate surface; exposing the substrate surface to a vapor comprisinga precursor having a structure represented by formula (I):

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup; and exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface. The precursormay be selected according to any of the embodiments listed above. In oneor more embodiments, the substrate comprises silicon. In one or moreembodiments, the substrate surface is exposed to the precursor andreductant gas substantially simultaneously or sequentially. As usedherein, “substantially simultaneously” refers to either co-flow or wherethere is merely overlap between exposures of the precursor andreductant. The reducing gas may comprise ammonia or hydrogen gas. Thereducing gas may comprise ammonia or hydrogen gas. In a particularembodiment, the film consisting essentially of nickel contains nonitrogen.

In one or more embodiments, the films deposited via the methodsdescribed herein are suitable for use in the production oflow-resistance, nickel silicide contacts because of reduced levels ofcarbon and/or oxygen contaminants. Once the nickel film is depositedover a silicon substrate, it can be converted to the silicide form byreaction with a silicon substrate. In one or more embodiments, this maybe achieved through annealing at slightly elevated temperatures, ifnecessary. However, in one or more embodiments, the temperature does notexceed about 250 to about 275° C., because of the possibility of theformation of the disilicide (NiSi₂), which is too electricallyresistive. In other embodiments, such as those relating toanti-corrosion coatings, there would not necessarily be this temperaturelimit.

While not wishing to be bound to any particular theory, it is thoughtthat when the substrate is exposed to the complex, the complexchemically decomposes the nickel into the film and produce vapor-phaseligands (or vapor-phase ligand decomposition products). Decomposition isachieved both by thermal cleavage of the metal-ligand bond and bycontacting the metal complex, or surface-bound ligands, with a reducinggas results in an exchange reaction between the metal coordinationcomplex and the reducing gas, thereby dissociating the bound organicligand and producing a first layer consisting essentially of nickel onthe surface of the substrate. The ligands can then be removed, and notincorporated into the film.

The substrate for deposition of the elemental thin layer films may beany substrate suitable for conformal film coating in an ALD or CVDprocess. Such substrates include silicon, silica or coated silicon,metal, metal oxide and metal nitride. In one aspect of the invention,the substrate is a semiconductor substrate.

In one or more embodiments, exposure of the substrate surface to thevapor comprising the precursor and the reducing gas occurs under anoxide-free environment. In further embodiments, the deposited filmcontains no oxygen incorporation (i.e., is oxide-free). Oxide-free filmsare achievable using the precursors and methods described herein becausethe ligands do not contain oxygen atoms.

The above metal coordination complexes can be used in ALD or CVDprocesses to deposit the films described herein. As used herein, thephrase “atomic layer deposition” is used interchangeably with “ALD,” andrefers to a process which involves sequential exposures of chemicalreactants, and each reactant is deposited from the other separated intime and space. However, according to one or more embodiments, thephrase “atomic layer deposition” is not necessarily limited to reactionsin which each reactant layer deposited is limited to a monolayer (i.e.,a layer that is one reactant molecule thick). Atomic layer deposition isdistinguished from “chemical vapor deposition” or “CVD,” in that CVDrefers to a process in which one or more reactants continuously form afilm on a substrate by reaction in a process chamber containing thesubstrate or on the surface of the substrate.

Accordingly, another aspect of the invention relates to a method ofdepositing a film consisting essentially of nickel via atomic layerdeposition. The method comprises providing a substrate surfacecomprising silicon, wherein the substrate surface has a temperatureranging from between about 120 and about 250° C.; sequentially exposingthe substrate surface to vapor comprising a precursor having a structurerepresented by formula (I):

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup; and exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface. Any of theabove variants in the metal coordination complex may be used. Forexample, in one embodiment, R² is methyl. In another embodiment, theprecursor is homoleptic.

Another aspect of the invention relates to a method of depositing a filmconsisting essentially of nickel via chemical vapor deposition. Themethod comprises providing a substrate surface comprising silicon;simultaneously exposing the substrate surface to a vapor comprising aprecursor having a structure represented by formula (I):

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup while exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface. Again, any ofthe above variants in the metal coordination complex may be used. Forexample, in one embodiment, R² is methyl. In another embodiment, theprecursor is homoleptic.

Optionally, a second layer may be formed on the first layer by repeatingany of the process reaction cycles described above. Any hydrocarbonremaining from the preceding reduction reaction or decomposition may bepurged from the deposition chamber using an inert gas. A metalcoordination complex in vapor phase is again flowed into thechamber/exposed to metal film on the substrate surface. An exchangereaction occurs between the metal coordination complex and hydrogen atthe metal surface of the first atomic layer. This displaces one of theligands from the vapor phase metal coordination complex and leaves themetal atom of the metal coordination complex bound to the metal atom ofthe first atomic layer. The reaction time, temperature and pressure areselected to create a metal-surface interaction and form a layer on thesurface of the substrate. Unreacted vapor phase metal coordinationcomplex and released ligand can then be purged from the depositionchamber using an insert gas. A reducing gas may again be flowed into thedeposition chamber to reduce the bond(s) between the metal and anyremaining ligand(s), releasing the remaining ligand(s) from the metalcenter and producing a second atomic layer of elemental metal on thefirst atomic layer of elemental metal. Additional repetitions of thedeposition cycle may be used to build a layer of elemental metal of thedesired thickness.

In one or more embodiments, the substrate surface has a temperature ofgreater than about 70, 80, 90 or 100° C. and less than about 250, 225,200 or 175° C. While not wishing to be bound to any particular theory,it is thought that low temperatures at which the process is able to becarried out prevents carbon incorporation.

The deposition can be carried out at atmospheric pressure but is morecommonly carried out at a reduced pressure. The vapor pressure of themetal coordination complex should be high enough to be practical in suchapplications.

In some embodiments, one or more layers may be formed during a plasmaenhanced atomic layer deposition (PEALD) process. In some processes, theuse of plasma provides sufficient energy to promote a species into theexcited state where surface reactions become favorable and likely.Introducing the plasma into the process can be continuous or pulsed. Insome embodiments, sequential pulses of precursors (or reactive gases)and plasma are used to process a layer. In some embodiments, thereagents may be ionized either locally (i.e., within the processingarea) or remotely (i.e., outside the processing area). In someembodiments, remote ionization can occur upstream of the depositionchamber such that ions or other energetic or light emitting species arenot in direct contact with the depositing film. In some PEALD processes,the plasma is generated external from the processing chamber, such as bya remote plasma generator system. The plasma may be generated via anysuitable plasma generation process or technique known to those skilledin the art. For example, plasma may be generated by one or more of amicrowave (MW) frequency generator or a radio frequency (RF) generator.The frequency of the plasma may be tuned depending on the specificreactive species being used. Suitable frequencies include, but are notlimited to, 2 MHz, 13.56 MHz, 40 MHz, 60 MHz and 100 MHz. Althoughplasmas may be used during the deposition processes disclosed herein, itshould be noted that plasmas may not required. Indeed, other embodimentsrelate to deposition processes under very mild conditions without aplasma.

According to one or more embodiments, the substrate is subjected toprocessing prior to and/or after forming the layer. This processing canbe performed in the same chamber or in one or more separate processingchambers. In some embodiments, the substrate is moved from the firstchamber to a separate, second chamber for further processing. Thesubstrate can be moved directly from the first chamber to the separateprocessing chamber, or it can be moved from the first chamber to one ormore transfer chambers, and then moved to the desired separateprocessing chamber. Accordingly, the processing apparatus may comprisemultiple chambers in communication with a transfer station. An apparatusof this sort may be referred to as a “cluster tool” or “clusteredsystem”, and the like.

Generally, a cluster tool is a modular system comprising multiplechambers which perform various functions including substratecenter-finding and orientation, degassing, annealing, deposition and/oretching. According to one or more embodiments, a cluster tool includesat least a first chamber and a central transfer chamber. The centraltransfer chamber may house a robot that can shuttle substrates betweenand among processing chambers and load lock chambers. The transferchamber is typically maintained at a vacuum condition and provides anintermediate stage for shuttling substrates from one chamber to anotherand/or to a load lock chamber positioned at a front end of the clustertool. Two well-known cluster tools which may be adapted for the presentinvention are the Centura® and the Endura®, both available from AppliedMaterials, Inc., of Santa Clara, Calif. The details of one suchstaged-vacuum substrate processing apparatus is disclosed in U.S. Pat.No. 5,186,718, entitled “Staged-Vacuum Wafer Processing Apparatus andMethod,” Tepman et al., issued on Feb. 16, 1993. However, the exactarrangement and combination of chambers may be altered for purposes ofperforming specific steps of a process as described herein. Otherprocessing chambers which may be used include, but are not limited to,cyclical layer deposition (CLD), atomic layer deposition (ALD), chemicalvapor deposition (CVD), physical vapor deposition (PVD), etch,pre-clean, chemical clean, thermal treatment such as RTP, plasmanitridation, degas, orientation, hydroxylation and other substrateprocesses. By carrying out processes in a chamber on a cluster tool,surface contamination of the substrate with atmospheric impurities canbe avoided without oxidation prior to depositing a subsequent film.

According to one or more embodiments, the substrate is continuouslyunder vacuum or “load lock” conditions, and is not exposed to ambientair when being moved from one chamber to the next. The transfer chambersare thus under vacuum and are “pumped down” under vacuum pressure. Inertgases may be present in the processing chambers or the transferchambers. In some embodiments, an inert gas is used as a purge gas toremove some or all of the reactants after forming the silicon layer onthe surface of the substrate.

As discussed above, in some embodiments, the deposited films areoxide-free. In further embodiments, deposition occurs without a break invacuum and/or without exposure to ambient conditions, thereby preventingexposure (and thus incorporation) of oxygen.

According to one or more embodiments, a purge gas is injected at theexit of the deposition chamber to prevent reactants from moving from thedeposition chamber to the transfer chamber and/or additional processingchamber. Thus, the flow of inert gas forms a curtain at the exit of thechamber.

The substrate can be processed in single substrate deposition chambers,where a single substrate is loaded, processed and unloaded beforeanother substrate is processed. The substrate can also be processed in acontinuous manner, like a conveyer system, in which multiple substrateare individually loaded into a first part of the chamber, move throughthe chamber and are unloaded from a second part of the chamber. Theshape of the chamber and associated conveyer system can form a straightpath or curved path. Additionally, the processing chamber may be acarousel in which multiple substrates are moved about a central axis andare exposed to deposition, etch, annealing, cleaning, etc. processesthroughout the carousel path.

During processing, the substrate can be heated or cooled. Such heatingor cooling can be accomplished by any suitable means including, but notlimited to, changing the temperature of the substrate support andflowing heated or cooled gases to the substrate surface. In someembodiments, the substrate support includes a heater/cooler which can becontrolled to change the substrate temperature conductively. In one ormore embodiments, the gases (either reactive gases or inert gases) beingemployed are heated or cooled to locally change the substratetemperature. In some embodiments, a heater/cooler is positioned withinthe chamber adjacent the substrate surface to convectively change thesubstrate temperature.

The substrate can also be stationary or rotated during processing. Arotating substrate can be rotated continuously or in discreet steps. Forexample, a substrate may be rotated throughout the entire process, orthe substrate can be rotated by a small amount between exposure todifferent reactive or purge gases. Rotating the substrate duringprocessing (either continuously or in steps) may help produce a moreuniform deposition or etch by minimizing the effect of, for example,local variability in gas flow geometries.

Example

FIG. 1 shows the thermogravimetric analysis of two metal coordinationcomplexes. One coordination complex contains a nickel atom with twocyclopentadienyl ligands that contain four methyl groups each((Me₈Cp)₂Ni). The other complex contains a nickel atom with two Cp*ligands ((Me₁₀Cp)₂Ni). The weight of the sample material for eachcomplex was measured as the material was exposed to increasingtemperature. As the temperature is increased, the complexes evaporate,which decreases the measured weight. FIG. 1 shows both the weight of thematerial as a function of time as well as the first derivative of theweight.

As can be seen from the data, the (Me₁₀Cp)₂Ni material decreased simplywith increasing temperature, indicating that with increasingtemperature, the complex evaporated. On the other hand, the ((Me₈Cp)₂Nicomplex shows a more complex pathway, indicating that the complexdecomposes to a certain extent. Indeed, the weight of the sample neverreaches zero, showing that decomposed material remains.

This relatively clean vaporization of (Me₁₀Cp)₂Ni compared to (Me₈Cp)₂Nidemonstrates that a lack of symmetry in the ligand introducesinstability. It is thought that this type of instability contributes tocontamination, particularly that of carbon, into the film. For example,with the ligand in (Me₈Cp)₂Ni, it is thought that the hydrogen on theunsubstituted carbon in the Cp ring is removed, such that the liganddecomposes to non-volatile species and carbon is available to beincorporated in to the film.

This concept can be extended to the coordination complexes of formula(I). Instead of the unsubstituted carbon in (Me₈Cp)₂Ni, there is anitrogen, thereby removing the pathway for decomposition. This thereforeallows in asymmetry in the ligand without substantial carboncontamination.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present invention without departing from the spirit andscope of the invention. Thus, it is intended that the present inventioninclude modifications and variations that are within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of depositing a film consistingessentially of nickel, the method comprising: providing a substratesurface; exposing the substrate surface to a vapor comprising aprecursor having a structure represented by:

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup; exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface.
 2. The methodof claim 1, wherein R² is methyl.
 3. The method of claim 1, wherein R²is C2 or C3 alkyl.
 4. The method of claim 1, wherein the precursor ishomoleptic.
 5. The method of claim 1, wherein the substrate comprisessilicon.
 6. The method of claim 1, wherein the substrate surface isexposed to the precursor and reductant gas substantially simultaneouslyor sequentially.
 7. The method of claim 1, wherein the reducing gascomprises ammonia gas or hydrogen gas.
 8. The method of claim 1, whereinthe film consisting essentially of nickel contains no oxygen.
 9. Amethod of depositing a film consisting essentially of nickel via atomiclayer deposition, the method comprising: providing a substrate surfacecomprising silicon, wherein the substrate surface has a temperatureranging from between about 120 and about 250° C.; sequentially exposingthe substrate surface to vapor comprising a precursor having a structurerepresented by:

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup; exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface.
 10. Themethod of claim 9, wherein R² is methyl.
 11. The method of claim 9,wherein exposure of the substrate surface to the vapor comprising theprecursor and the reducing gas occurs under an oxide-free environment.12. The method of claim 9, wherein the precursor is homoleptic.
 13. Themethod of claim 9, wherein the reducing gas comprises ammonia gas orhydrogen gas.
 14. The method of claim 9, wherein the film consistingessentially of nickel is oxide-free and contains less than about 5%carbon.
 15. A method of depositing a film consisting essentially ofnickel via chemical vapor deposition, the method comprising: providing asubstrate surface comprising silicon; simultaneously exposing thesubstrate surface to a vapor comprising a precursor having a structurerepresented by:

wherein R¹ is t-butyl and each R² is each independently any C1-C3 alkylgroup while exposing the substrate to a reducing gas to provide a filmconsisting essentially of nickel on the substrate surface.
 16. Themethod of claim 15, wherein R² is methyl.
 17. The method of claim 15,wherein exposure of the substrate surface to the vapor comprising theprecursor and the reducing gas occurs under an oxide-free environment.18. The method of claim 15, wherein the precursor is homoleptic.
 19. Themethod of claim 15, wherein the reducing gas comprises ammonia gas orhydrogen gas.
 20. The method of claim 15, wherein the film consistingessentially of nickel is oxide free and contains less than about 5%carbon.